1. Field of the Invention
This invention relates to apparatus for controlling speed of a vehicle.
2. Description of the Prior Art
An apparatus for controlling speed of a vehicle to consist speed with a target speed is disclosed in Japanese patent publication 62-36889. In this prior art apparatus, when vehicle speed decreases by a first predetermined deviation from a target speed in constant speed traveling mode, i.e., cruising mode, on an uphill road, a power transmission is changed from fourth, i.e., overdriving, to third gear positions automatically to recover vehicle speed. Then, the power transmission is changed to fourth gear position again after a predetermined interval has passed from an instant when vehicle speed recovers to a second predetermined deviation from the target speed, the second predetermined deviation being smaller than the first predetermined deviation.
According to such apparatus, frequency of changing gear position of the transmission is suppressed, so that driving feeling is improved to some extent. However, if the predetermined interval is short in consideration with length of an uphill road, periodical gear changes between higher gear to lower gear positions occurs. On the other hand, when the predetermined interval is short in consideration with length of an uphill road, the vehicle runs with lower gear position even if the road condition changed from the uphill road to a level road for some time.